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 $184.67   5.352%   $194.5535   $194.55   $194.55   $194.60  
  Purchase #2 $90.77   10.849%   $100.6176   $100.62   $100.60   $100.60  
  Purchase #3 $12.58   12.521%   $14.1551   $14.16   $14.15   $14.20  
  Purchase #4 $204.28   11.862%   $228.5117   $228.51   $228.50   $228.50  
  Purchase #5 $238.35   8.839%   $259.4178   $259.42   $259.40   $259.40  
  Purchase #6 $52.31   8.447%   $56.7286   $56.73   $56.75   $56.70  
  Purchase #7 $177.32   9.633%   $194.4012   $194.40   $194.40   $194.40  
  7 purchase totals = $960.28       $1,048.3855   $1,048.39   $1,048.35   $1,048.40