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 $148.57   11.789%   $166.0849   $166.08   $166.10   $166.10  
  Purchase #2 $246.53   9.167%   $269.1294   $269.13   $269.15   $269.10  
  Purchase #3 $241.54   12.647%   $272.0876   $272.09   $272.10   $272.10  
  Purchase #4 $83.67   4.549%   $87.4761   $87.48   $87.50   $87.50  
  Purchase #5 $169.95   5.630%   $179.5182   $179.52   $179.50   $179.50  
  Purchase #6 $148.25   9.289%   $162.0209   $162.02   $162.00   $162.00  
  Purchase #7 $225.56   3.349%   $233.114   $233.11   $233.10   $233.10  
  7 purchase totals = $1,264.07       $1,369.4311   $1,369.43   $1,369.45   $1,369.40