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 $204.83   11.862%   $229.1269   $229.13   $229.15   $229.10  
  Purchase #2 $63.91   12.283%   $71.7601   $71.76   $71.75   $71.80  
  Purchase #3 $115.28   8.744%   $125.3601   $125.36   $125.35   $125.40  
  Purchase #4 $108.83   6.236%   $115.6166   $115.62   $115.60   $115.60  
  Purchase #5 $93.45   12.616%   $105.2397   $105.24   $105.25   $105.20  
  Purchase #6 $175.53   3.417%   $181.5279   $181.53   $181.55   $181.50  
  Purchase #7 $7.31   10.581%   $8.0835   $8.08   $8.10   $8.10  
  7 purchase totals = $769.14       $836.7148   $836.72   $836.75   $836.70