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 $46.94   11.556%   $52.3644   $52.36   $52.35   $52.40  
  Purchase #2 $234.64   8.548%   $254.697   $254.70   $254.70   $254.70  
  Purchase #3 $99.61   7.753%   $107.3328   $107.33   $107.35   $107.30  
  Purchase #4 $222.76   10.415%   $245.9605   $245.96   $245.95   $246.00  
  Purchase #5 $63.74   7.782%   $68.7002   $68.70   $68.70   $68.70  
  Purchase #6 $152.37   13.359%   $172.7251   $172.73   $172.75   $172.70  
  Purchase #7 $34.50   5.822%   $36.5086   $36.51   $36.50   $36.50  
  7 purchase totals = $854.56       $938.2886   $938.29   $938.30   $938.30