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 $83.93   3.143%   $86.5679   $86.57   $86.55   $86.60  
  Purchase #2 $152.56   11.226%   $169.6864   $169.69   $169.70   $169.70  
  Purchase #3 $65.38   12.818%   $73.7604   $73.76   $73.75   $73.80  
  Purchase #4 $181.37   9.411%   $198.4387   $198.44   $198.45   $198.40  
  Purchase #5 $219.35   12.389%   $246.5253   $246.53   $246.55   $246.50  
  Purchase #6 $39.52   3.297%   $40.823   $40.82   $40.80   $40.80  
  Purchase #7 $126.96   9.289%   $138.7533   $138.75   $138.75   $138.80  
  7 purchase totals = $869.07       $954.5550   $954.56   $954.55   $954.60