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 $80.83   13.767%   $91.9579   $91.96   $91.95   $92.00  
  Purchase #2 $91.29   7.133%   $97.8017   $97.80   $97.80   $97.80  
  Purchase #3 $121.77   11.479%   $135.748   $135.75   $135.75   $135.70  
  Purchase #4 $228.66   5.250%   $240.6647   $240.66   $240.65   $240.70  
  Purchase #5 $60.30   9.287%   $65.9001   $65.90   $65.90   $65.90  
  Purchase #6 $134.86   11.335%   $150.1464   $150.15   $150.15   $150.10  
  Purchase #7 $203.77   3.381%   $210.6595   $210.66   $210.65   $210.70  
  7 purchase totals = $921.48       $992.8783   $992.88   $992.85   $992.90