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 $167.58   11.361%   $186.6188   $186.62   $186.60   $186.60  
  Purchase #2 $62.84   8.702%   $68.3083   $68.31   $68.30   $68.30  
  Purchase #3 $123.71   6.410%   $131.6398   $131.64   $131.65   $131.60  
  Purchase #4 $237.53   6.720%   $253.492   $253.49   $253.50   $253.50  
  Purchase #5 $139.52   8.784%   $151.7754   $151.78   $151.80   $151.80  
  Purchase #6 $59.28   6.829%   $63.3282   $63.33   $63.35   $63.30  
  Purchase #7 $189.55   7.345%   $203.4724   $203.47   $203.45   $203.50  
  7 purchase totals = $980.01       $1,058.6349   $1,058.64   $1,058.65   $1,058.60