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 $188.74   8.774%   $205.3   $205.30   $205.30   $205.30  
  Purchase #2 $116.95   3.253%   $120.7544   $120.75   $120.75   $120.80  
  Purchase #3 $37.88   3.809%   $39.3228   $39.32   $39.30   $39.30  
  Purchase #4 $207.72   8.808%   $226.016   $226.02   $226.00   $226.00  
  Purchase #5 $90.78   5.558%   $95.8256   $95.83   $95.85   $95.80  
  Purchase #6 $145.35   7.107%   $155.68   $155.68   $155.70   $155.70  
  Purchase #7 $140.39   6.607%   $149.6656   $149.67   $149.65   $149.70  
  7 purchase totals = $927.81       $992.5644   $992.57   $992.55   $992.60