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 $216.60   13.715%   $246.3067   $246.31   $246.30   $246.30  
  Purchase #2 $176.94   6.450%   $188.3526   $188.35   $188.35   $188.40  
  Purchase #3 $59.61   11.678%   $66.5713   $66.57   $66.55   $66.60  
  Purchase #4 $85.55   6.576%   $91.1758   $91.18   $91.20   $91.20  
  Purchase #5 $184.39   9.108%   $201.1842   $201.18   $201.20   $201.20  
  Purchase #6 $102.77   13.492%   $116.6357   $116.64   $116.65   $116.60  
  Purchase #7 $249.27   3.272%   $257.4261   $257.43   $257.45   $257.40  
  7 purchase totals = $1,075.13       $1,167.6524   $1,167.66   $1,167.70   $1,167.70