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 $79.67   11.182%   $88.5787   $88.58   $88.60   $88.60  
  Purchase #2 $189.58   8.162%   $205.0535   $205.05   $205.05   $205.10  
  Purchase #3 $167.53   13.865%   $190.758   $190.76   $190.75   $190.80  
  Purchase #4 $249.53   7.415%   $268.0326   $268.03   $268.05   $268.00  
  Purchase #5 $169.98   10.245%   $187.3945   $187.39   $187.40   $187.40  
  Purchase #6 $31.46   12.208%   $35.3006   $35.30   $35.30   $35.30  
  Purchase #7 $97.48   11.743%   $108.9271   $108.93   $108.95   $108.90  
  7 purchase totals = $985.23       $1,084.0450   $1,084.04   $1,084.10   $1,084.10