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 $78.85   6.473%   $83.954   $83.95   $83.95   $84.00  
  Purchase #2 $220.56   11.731%   $246.4339   $246.43   $246.45   $246.40  
  Purchase #3 $209.53   9.653%   $229.7559   $229.76   $229.75   $229.80  
  Purchase #4 $77.66   8.394%   $84.1788   $84.18   $84.20   $84.20  
  Purchase #5 $212.26   11.444%   $236.551   $236.55   $236.55   $236.60  
  Purchase #6 $207.89   13.562%   $236.084   $236.08   $236.10   $236.10  
  Purchase #7 $106.35   11.556%   $118.6398   $118.64   $118.65   $118.60  
  7 purchase totals = $1,113.10       $1,235.5974   $1,235.59   $1,235.65   $1,235.70