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 $23.52   8.590%   $25.5404   $25.54   $25.55   $25.50  
  Purchase #2 $88.48   4.350%   $92.3289   $92.33   $92.35   $92.30  
  Purchase #3 $59.94   5.581%   $63.2853   $63.29   $63.30   $63.30  
  Purchase #4 $72.25   10.362%   $79.7365   $79.74   $79.75   $79.70  
  Purchase #5 $210.80   4.400%   $220.0752   $220.08   $220.10   $220.10  
  Purchase #6 $179.28   11.637%   $200.1428   $200.14   $200.15   $200.10  
  Purchase #7 $236.58   11.573%   $263.9594   $263.96   $263.95   $264.00  
  7 purchase totals = $870.85       $945.0685   $945.08   $945.15   $945.00