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 $84.56   9.302%   $92.4258   $92.43   $92.45   $92.40  
  Purchase #2 $181.27   3.332%   $187.3099   $187.31   $187.30   $187.30  
  Purchase #3 $180.29   11.331%   $200.7187   $200.72   $200.70   $200.70  
  Purchase #4 $250.42   6.134%   $265.7808   $265.78   $265.80   $265.80  
  Purchase #5 $27.97   4.638%   $29.2672   $29.27   $29.25   $29.30  
  Purchase #6 $42.75   13.527%   $48.5328   $48.53   $48.55   $48.50  
  Purchase #7 $188.42   7.585%   $202.7117   $202.71   $202.70   $202.70  
  7 purchase totals = $955.68       $1,026.7469   $1,026.75   $1,026.75   $1,026.70