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 $34.73   7.816%   $37.4445   $37.44   $37.45   $37.40  
  Purchase #2 $139.84   8.536%   $151.7767   $151.78   $151.80   $151.80  
  Purchase #3 $59.80   6.817%   $63.8766   $63.88   $63.90   $63.90  
  Purchase #4 $38.41   6.778%   $41.0134   $41.01   $41.00   $41.00  
  Purchase #5 $80.30   7.751%   $86.5241   $86.52   $86.50   $86.50  
  Purchase #6 $202.37   5.443%   $213.385   $213.39   $213.40   $213.40  
  Purchase #7 $204.55   7.142%   $219.159   $219.16   $219.15   $219.20  
  7 purchase totals = $760.00       $813.1793   $813.18   $813.20   $813.20