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 $88.58   9.511%   $97.0048   $97.00   $97.00   $97.00  
  Purchase #2 $34.81   8.733%   $37.85   $37.85   $37.85   $37.90  
  Purchase #3 $59.30   3.201%   $61.1982   $61.20   $61.20   $61.20  
  Purchase #4 $58.81   11.435%   $65.5349   $65.53   $65.55   $65.50  
  Purchase #5 $116.85   5.855%   $123.6916   $123.69   $123.70   $123.70  
  Purchase #6 $226.56   6.411%   $241.0848   $241.08   $241.10   $241.10  
  Purchase #7 $156.53   9.673%   $171.6711   $171.67   $171.65   $171.70  
  7 purchase totals = $741.44       $798.0354   $798.02   $798.05   $798.10