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 $55.91   12.304%   $62.7892   $62.79   $62.80   $62.80  
  Purchase #2 $249.52   10.638%   $276.0639   $276.06   $276.05   $276.10  
  Purchase #3 $154.42   8.622%   $167.7341   $167.73   $167.75   $167.70  
  Purchase #4 $175.90   11.430%   $196.0054   $196.01   $196.00   $196.00  
  Purchase #5 $79.62   11.652%   $88.8973   $88.90   $88.90   $88.90  
  Purchase #6 $204.64   11.424%   $228.0181   $228.02   $228.00   $228.00  
  Purchase #7 $88.86   13.301%   $100.6793   $100.68   $100.70   $100.70  
  7 purchase totals = $1,008.87       $1,120.1873   $1,120.19   $1,120.20   $1,120.20