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 $24.86   3.581%   $25.7502   $25.75   $25.75   $25.80  
  Purchase #2 $43.39   12.768%   $48.93   $48.93   $48.95   $48.90  
  Purchase #3 $41.36   10.739%   $45.8017   $45.80   $45.80   $45.80  
  Purchase #4 $105.39   4.384%   $110.0103   $110.01   $110.00   $110.00  
  Purchase #5 $29.90   10.629%   $33.0781   $33.08   $33.10   $33.10  
  Purchase #6 $5.41   6.107%   $5.7404   $5.74   $5.75   $5.70  
  Purchase #7 $87.26   6.714%   $93.1186   $93.12   $93.10   $93.10  
  7 purchase totals = $337.57       $362.4293   $362.43   $362.45   $362.40