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 $55.88   12.803%   $63.0343   $63.03   $63.05   $63.00  
  Purchase #2 $131.58   4.716%   $137.7853   $137.79   $137.80   $137.80  
  Purchase #3 $160.28   12.584%   $180.4496   $180.45   $180.45   $180.40  
  Purchase #4 $247.37   6.576%   $263.6371   $263.64   $263.65   $263.60  
  Purchase #5 $234.84   4.640%   $245.7366   $245.74   $245.75   $245.70  
  Purchase #6 $243.36   10.259%   $268.3263   $268.33   $268.35   $268.30  
  Purchase #7 $11.30   4.729%   $11.8344   $11.83   $11.85   $11.80  
  7 purchase totals = $1,084.61       $1,170.8036   $1,170.81   $1,170.90   $1,170.60