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 $53.89   5.126%   $56.6524   $56.65   $56.65   $56.70  
  Purchase #2 $210.36   11.656%   $234.8796   $234.88   $234.90   $234.90  
  Purchase #3 $27.85   11.639%   $31.0915   $31.09   $31.10   $31.10  
  Purchase #4 $203.45   7.809%   $219.3374   $219.34   $219.35   $219.30  
  Purchase #5 $231.48   3.146%   $238.7624   $238.76   $238.75   $238.80  
  Purchase #6 $92.60   4.758%   $97.0059   $97.01   $97.00   $97.00  
  Purchase #7 $118.59   13.873%   $135.042   $135.04   $135.05   $135.00  
  7 purchase totals = $938.22       $1,012.7712   $1,012.77   $1,012.80   $1,012.80