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 $87.94   11.343%   $97.915   $97.92   $97.90   $97.90  
  Purchase #2 $139.43   12.740%   $157.1934   $157.19   $157.20   $157.20  
  Purchase #3 $85.85   12.145%   $96.2765   $96.28   $96.30   $96.30  
  Purchase #4 $232.36   8.760%   $252.7147   $252.71   $252.70   $252.70  
  Purchase #5 $238.97   12.179%   $268.0742   $268.07   $268.05   $268.10  
  Purchase #6 $167.97   9.362%   $183.6954   $183.70   $183.70   $183.70  
  Purchase #7 $184.79   5.529%   $195.007   $195.01   $195.00   $195.00  
  7 purchase totals = $1,137.31       $1,250.8762   $1,250.88   $1,250.85   $1,250.90