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 $135.29   8.849%   $147.2618   $147.26   $147.25   $147.30  
  Purchase #2 $202.59   4.388%   $211.4796   $211.48   $211.50   $211.50  
  Purchase #3 $110.57   4.588%   $115.643   $115.64   $115.65   $115.60  
  Purchase #4 $193.95   4.555%   $202.7844   $202.78   $202.80   $202.80  
  Purchase #5 $180.56   4.317%   $188.3548   $188.35   $188.35   $188.40  
  Purchase #6 $145.84   3.715%   $151.258   $151.26   $151.25   $151.30  
  Purchase #7 $27.44   6.369%   $29.1877   $29.19   $29.20   $29.20  
  7 purchase totals = $996.24       $1,045.9693   $1,045.96   $1,046.00   $1,046.10