Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $102.48   13.736%   $116.5567   $116.56   $116.55   $116.60  
  Purchase #2 $147.35   13.132%   $166.7   $166.70   $166.70   $166.70  
  Purchase #3 $131.81   13.598%   $149.7335   $149.73   $149.75   $149.70  
  Purchase #4 $188.67   12.109%   $211.5161   $211.52   $211.50   $211.50  
  Purchase #5 $178.48   8.521%   $193.6883   $193.69   $193.70   $193.70  
  Purchase #6 $145.87   4.214%   $152.017   $152.02   $152.00   $152.00  
  Purchase #7 $238.27   10.250%   $262.6927   $262.69   $262.70   $262.70  
  7 purchase totals = $1,132.93       $1,252.9043   $1,252.91   $1,252.90   $1,252.90