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 $244.33   8.670%   $265.5134   $265.51   $265.50   $265.50  
  Purchase #2 $14.78   7.802%   $15.9331   $15.93   $15.95   $15.90  
  Purchase #3 $60.99   10.610%   $67.461   $67.46   $67.45   $67.50  
  Purchase #4 $39.44   11.687%   $44.0494   $44.05   $44.05   $44.00  
  Purchase #5 $212.61   8.222%   $230.0908   $230.09   $230.10   $230.10  
  Purchase #6 $202.52   4.294%   $211.2162   $211.22   $211.20   $211.20  
  Purchase #7 $184.53   8.669%   $200.5269   $200.53   $200.55   $200.50  
  7 purchase totals = $959.20       $1,034.7908   $1,034.79   $1,034.80   $1,034.70