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 $152.83   10.780%   $169.3051   $169.31   $169.30   $169.30  
  Purchase #2 $189.74   11.748%   $212.0307   $212.03   $212.05   $212.00  
  Purchase #3 $5.54   8.195%   $5.994   $5.99   $6.00   $6.00  
  Purchase #4 $62.40   4.785%   $65.3858   $65.39   $65.40   $65.40  
  Purchase #5 $68.67   10.170%   $75.6537   $75.65   $75.65   $75.70  
  Purchase #6 $203.50   4.453%   $212.5619   $212.56   $212.55   $212.60  
  Purchase #7 $58.52   7.309%   $62.7972   $62.80   $62.80   $62.80  
  7 purchase totals = $741.20       $803.7284   $803.73   $803.75   $803.80