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 $179.29   10.725%   $198.5189   $198.52   $198.50   $198.50  
  Purchase #2 $145.83   4.690%   $152.6694   $152.67   $152.65   $152.70  
  Purchase #3 $138.59   12.498%   $155.911   $155.91   $155.90   $155.90  
  Purchase #4 $21.52   5.333%   $22.6677   $22.67   $22.65   $22.70  
  Purchase #5 $200.61   8.361%   $217.383   $217.38   $217.40   $217.40  
  Purchase #6 $235.44   10.668%   $260.5567   $260.56   $260.55   $260.60  
  Purchase #7 $212.91   9.791%   $233.756   $233.76   $233.75   $233.80  
  7 purchase totals = $1,134.19       $1,241.4627   $1,241.47   $1,241.40   $1,241.60