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 $160.28   13.166%   $181.3825   $181.38   $181.40   $181.40  
  Purchase #2 $185.52   11.307%   $206.4967   $206.50   $206.50   $206.50  
  Purchase #3 $10.28   13.478%   $11.6655   $11.67   $11.65   $11.70  
  Purchase #4 $85.84   7.751%   $92.4935   $92.49   $92.50   $92.50  
  Purchase #5 $156.38   6.232%   $166.1256   $166.13   $166.15   $166.10  
  Purchase #6 $239.52   4.871%   $251.187   $251.19   $251.20   $251.20  
  Purchase #7 $104.47   11.849%   $116.8487   $116.85   $116.85   $116.80  
  7 purchase totals = $942.29       $1,026.1995   $1,026.21   $1,026.25   $1,026.20