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 $119.28   7.263%   $127.9433   $127.94   $127.95   $127.90  
  Purchase #2 $150.99   13.269%   $171.0249   $171.02   $171.00   $171.00  
  Purchase #3 $48.57   12.623%   $54.701   $54.70   $54.70   $54.70  
  Purchase #4 $215.32   10.790%   $238.553   $238.55   $238.55   $238.60  
  Purchase #5 $165.55   5.117%   $174.0212   $174.02   $174.00   $174.00  
  Purchase #6 $151.49   6.232%   $160.9309   $160.93   $160.95   $160.90  
  Purchase #7 $28.30   4.324%   $29.5237   $29.52   $29.50   $29.50  
  7 purchase totals = $879.50       $956.6980   $956.68   $956.65   $956.60