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 $119.35   7.516%   $128.3203   $128.32   $128.30   $128.30  
  Purchase #2 $33.35   9.107%   $36.3872   $36.39   $36.40   $36.40  
  Purchase #3 $160.32   8.865%   $174.5324   $174.53   $174.55   $174.50  
  Purchase #4 $208.46   8.125%   $225.3974   $225.40   $225.40   $225.40  
  Purchase #5 $235.98   13.494%   $267.8231   $267.82   $267.80   $267.80  
  Purchase #6 $53.60   9.188%   $58.5248   $58.52   $58.50   $58.50  
  Purchase #7 $161.40   11.821%   $180.4791   $180.48   $180.50   $180.50  
  7 purchase totals = $972.46       $1,071.4643   $1,071.46   $1,071.45   $1,071.40