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 $177.65   11.478%   $198.0407   $198.04   $198.05   $198.00  
  Purchase #2 $213.86   6.798%   $228.3982   $228.40   $228.40   $228.40  
  Purchase #3 $240.29   12.655%   $270.6987   $270.70   $270.70   $270.70  
  Purchase #4 $78.93   5.860%   $83.5553   $83.56   $83.55   $83.60  
  Purchase #5 $132.96   11.445%   $148.1773   $148.18   $148.20   $148.20  
  Purchase #6 $96.68   13.596%   $109.8246   $109.82   $109.80   $109.80  
  Purchase #7 $22.39   10.852%   $24.8198   $24.82   $24.80   $24.80  
  7 purchase totals = $962.76       $1,063.5146   $1,063.52   $1,063.50   $1,063.50