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 $43.64   13.513%   $49.5371   $49.54   $49.55   $49.50  
  Purchase #2 $234.41   3.174%   $241.8502   $241.85   $241.85   $241.90  
  Purchase #3 $212.38   8.281%   $229.9672   $229.97   $229.95   $230.00  
  Purchase #4 $243.52   13.124%   $275.4796   $275.48   $275.50   $275.50  
  Purchase #5 $80.62   8.350%   $87.3518   $87.35   $87.35   $87.40  
  Purchase #6 $131.25   11.349%   $146.1456   $146.15   $146.15   $146.10  
  Purchase #7 $39.35   12.869%   $44.414   $44.41   $44.40   $44.40  
  7 purchase totals = $985.17       $1,074.7455   $1,074.75   $1,074.75   $1,074.80