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 $61.45   12.259%   $68.9832   $68.98   $69.00   $69.00  
  Purchase #2 $181.49   11.179%   $201.7788   $201.78   $201.80   $201.80  
  Purchase #3 $118.94   5.779%   $125.8135   $125.81   $125.80   $125.80  
  Purchase #4 $212.52   10.648%   $235.1491   $235.15   $235.15   $235.10  
  Purchase #5 $115.92   9.589%   $127.0356   $127.04   $127.05   $127.00  
  Purchase #6 $84.72   10.640%   $93.7342   $93.73   $93.75   $93.70  
  Purchase #7 $88.68   5.825%   $93.8456   $93.85   $93.85   $93.80  
  7 purchase totals = $863.72       $946.3400   $946.34   $946.40   $946.20