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 $11.29   6.472%   $12.0207   $12.02   $12.00   $12.00  
  Purchase #2 $141.74   4.165%   $147.6435   $147.64   $147.65   $147.60  
  Purchase #3 $238.84   4.718%   $250.1085   $250.11   $250.10   $250.10  
  Purchase #4 $155.89   5.352%   $164.2332   $164.23   $164.25   $164.20  
  Purchase #5 $46.52   6.288%   $49.4452   $49.45   $49.45   $49.40  
  Purchase #6 $102.79   13.514%   $116.681   $116.68   $116.70   $116.70  
  Purchase #7 $231.73   12.192%   $259.9825   $259.98   $260.00   $260.00  
  7 purchase totals = $928.80       $1,000.1146   $1,000.11   $1,000.15   $1,000.00