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 $85.68   6.600%   $91.3349   $91.33   $91.35   $91.30  
  Purchase #2 $189.26   6.709%   $201.9575   $201.96   $201.95   $202.00  
  Purchase #3 $65.98   6.528%   $70.2872   $70.29   $70.30   $70.30  
  Purchase #4 $247.36   3.650%   $256.3886   $256.39   $256.40   $256.40  
  Purchase #5 $86.78   10.652%   $96.0238   $96.02   $96.00   $96.00  
  Purchase #6 $186.76   12.335%   $209.7968   $209.80   $209.80   $209.80  
  Purchase #7 $127.83   5.685%   $135.0971   $135.10   $135.10   $135.10  
  7 purchase totals = $989.65       $1,060.8859   $1,060.89   $1,060.90   $1,060.90